Carbon-concentrating mechanisms in seagrasses

Anthony William D. Larkum (Lead / Corresponding author), Peter A. Davey, John Kuo, Peter J. Ralph, John A. Raven

Research output: Contribution to journalReview article

14 Citations (Scopus)

Abstract

Seagrasses are unique angiosperms that carry out growth and reproduction submerged in seawater. They occur in at least three families of the Alismatales. All have chloroplasts mainly in the cells of the epidermis. Living in seawater, the supply of inorganic carbon (Ci) to the chloroplasts is diffusion limited, especially under unstirred conditions. Therefore, the supply of CO2 and bicarbonate across the diffusive boundary layer on the outer side of the epidermis is often a limiting factor. Here we discuss the evidence for mechanisms that enhance the uptake of Ci into the epidermal cells. Since bicarbonate is plentiful in seawater, a bicarbonate pump might be expected; however, the evidence for such a pump is not strongly supported. There is evidence for a carbonic anhydrase outside the outer plasmalemma. This, together with evidence for an outward proton pump, suggests the possibility that local acidification leads to enhanced concentrations of CO2 adjacent to the outer tangential epidermal walls, which enhances the uptake of CO2, and this could be followed by a carbon-concentrating mechanism (CCM) in the cytoplasm and/or chloroplasts. The lines of evidence for such an epidermal CCM are discussed, including evidence for special 'transfer cells' in some but not all seagrass leaves in the tangential inner walls of the epidermal cells. It is concluded that seagrasses have a CCM but that the case for concentration of CO2 at the site of Rubisco carboxylation is not proven.

Original languageEnglish
Pages (from-to)3773-3784
Number of pages12
JournalJournal of Experimental Botany
Volume68
Issue number14
DOIs
Publication statusPublished - 1 Jul 2017

Keywords

  • Alismatales
  • Carbon-concentrating mechanisms
  • C4 metabolism
  • Diffusive boundary layers
  • Photosynthesis
  • Seagrasses

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    Larkum, A. W. D., Davey, P. A., Kuo, J., Ralph, P. J., & Raven, J. A. (2017). Carbon-concentrating mechanisms in seagrasses. Journal of Experimental Botany, 68(14), 3773-3784. https://doi.org/10.1093/jxb/erx206